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Disease Control and Pest Management

Reduction of Pseudomonas syringae pv. morsprunorum on Montmorency Sour Cherry with Copper and Dynamics of the Copper Residues. B. D. Olson, Graduate research assistant, Department of Botany and Plant Pathology and the Pesticide Research Center, Michigan State University, East Lansing 48824; A. L. Jones, professor, Department of Botany and Plant Pathology and the Pesticide Research Center, Michigan State University, East Lansing 48824. Phytopathology 73:1520-1525. Accepted for publication 17 May 1983. Copyright 1983 The American Phytopathological Society. DOI: 10.1094/Phyto-73-1520.

A rifampicin-resistant strain of P. syringae pv. morsprunorum (PsmR) was used to study the effectiveness of tribasic copper sulfate (TBS) and 48% copper salts of fatty and rosin acids (Citcop 4E) for reducing populations of PsmR on Montmorency sour cherry trees in spring and early summer. Populations of PsmR were reduced more by 636 and 949 mg of TBS per liter than by 200 mg of Citcop 4E per liter, but several applications were needed to reduce the populations to a low level. Citcop 4E at 200 mg/L was more phytotoxic to cherry foliage than TBS at 636 mg/L. Phytotoxicity was related to the number of applications and was not reduced by adding hydrated lime to the copper treatments. The loss of copper residues from leaves was related by multiple regression analyses to rainfall and the initial level of copper on leaves.